Native toplevel test release 3.12.1+ocamlnatjit2

After several additional hours of testing and bugfixing it was time for another test release of our new OCaml native code toplevel ocamlnat. The test release includes a fully featured OCaml 3.12.1 distribution plus our new toplevel ocamlnat, which is up to 100 times faster than the byte code toplevel. See the website for installation instructions and additional information.